Xerographic toner dispensing apparatus



Aug. 13, 1968 D. J. DONALIES 3,396,700

I XEROGRAPHIC TONER DISPENSING APPARATUS Filed Aug. 9, 1-967 INVENTOR.DANIEL J. DONALI ES BY qz A T TORNE Y5 United States Patent 0 3,396 700XEROGRAPHIC TONER D ISPENSHNG APPARATUS Daniel J. Donalies, Rochester,N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation ofNew York Filed Aug. 9, 1967, Ser. No. 659,519 10 Claims. (Cl. 118-637)ABSTRACT 0F THE DISCLGSURE Apparatus for dispensing toner particles toundertoned carrier granules in a xerographic development system, as ofthe fluidized bed type. A quantity of carrier granules to be toned ispassed through a toning zone bounded by a pair of screens, at least oneof which is electrically biased. Charged toner particles are held insuspension between the screens as by vibration. The carrier granules tobe toned triboelectrically attract and retain toner particles from thetoning zone, only up to the point of optimum toner concentration sincethe electric field within the zone acts as a competing force againstwhich the carrier granules rnust act in order to attract and retainadditional toner particles.

Background of the invention This invention relates in general tocontrolling the amount of toner particles on carrier beads in twocomponent xerographic development systems and in partic- I No. 2,297,691to Chester F. Carlson, a xerographic surface comprising a layer ofphotoconductive insulating material afiixed to a conductive backing isused to support electrostatic images. In the usual method of carryingout the process, the xerographic surface is electrostatically chargeduniformly over its surface and then exposed to a light pattern of theimage being reproduced to thereby discharge the charge in the areaswhere light strikes the layer. The undischarged areas of the layer thusform an electrostatic charge pattern in conformity with theconfiguration of the original light pattern.

The latent electrostatic image can then be developed by contacting itwith a finely divided electrostatical-ly attractable material such as apowder. The powder is held in image areas by the electrostatic chargeson the layer. Where the charge is greatest, the greatest amount ofmaterial is deposited; Where the charge is least, little or no materialis deposited. Thus a powder image is produced in conformity with thelight image of copy being reproduced. The powder is subsequentlytransferred to a sheet of paper or other surface and suitably affixedthereto to form a permanent print.

The electrostatically attractable developing material commonly used inxerography consists of a pigmented resinous powder referred to herein astoner and a coarse granular material called carrier. The carrier iscoated with a material removed in the triboelectric series from thetoner so that a charge is generated between the powder and the granularcarrier upon mutual interaction. Such charge causes the powder to adhereto the carrier. The carrier, besides providing a charge to the toner,permits mechanical control so that the toner can readily be brought intocontact with the exposed xerographic surface. The powder particles areattracted to the electrostatic image from the granular material toproduce a visible powder image on the xerographic surface.

The quality of the developed image may be aifected by the ratio of tonerparticles to carrier beads used for development, or, as this ratio iscommonly called, the toner concentration. For example, if there is adeficiency of toner, the image areas will be unable to attractsufiicient toner to fully develop the image, henoe, undesirably lightimages result. On the other hand, if there is an excess amount of tonerin a development system, the image areas become overly dark withquantities of toner becoming attached to non-image areas. This isbecause the attractive force holding the toner particles on a carrierhead is inversely proportional to the number of particles on such bead.Consequently, if there are few toner particles on a carrier bead, suchparticles will be strongly attracted thereto, and will not be readilygiven up to the charge of the image areas. If excess toner particles areon a carrier bead, the mutual attraction is decreased often to the pointwhere the residual charge on non-image areas is sufficient to attractthe toner particles from their associated carrier beads.

In the past, various attempts have been made to control the ratio oftoner to carrier in the developer. These attempts have generally havebeen directed to the periodic addition of raw toner into the developermix to supplant the toner lost from the system by its deposition on theimage. Various systems have accomplished this by adding tonerperiodically to the developer mixture on the basis of a time :cycle orsome suitable apparatus which automatically measures the developercharacteristics directly or the density of the developed image. Then inresponse to the information measured, a suitable amount of toner may beadded to the system.

While such systems are somewhat satisfactory, they have certain obviousshortcomings. For example, when toner is added to the developer it isgenerally added equally across the length of the development zone. If,however, the image being reproduced has large dark sections in one area,as the middle, then the central portions of the developer mix would bereduced to a lesser toner concentration than the side portion. Theaddition of toner to the developer evenly across the length of thedevelopment zone would not rectify this imbalance. Furthermore, systemsof the known type which are somewhat self-regulating generally need timeto react to a sudden depletion of toner caused by the development oflarge dense image areas. Hence, this time delay might cause sporadicdensity of development. This problem can be aggravated in some types ofthe time regulated toner dispensers. While these problems are not overlycritical today it appears that they will become magnified in the futuredue to increasing speeds and the advent of improved solid areacapabilities.

Known xerographic toner dispensing mechanisms generally permit carriergranules to accept toner particles until the individual carrier granulescan triboelectrically attract and retain no more toner. As carriergranules triboelectically attract and retain additional toner to theirsurfaces, their electrostatic attraction for additional toner particlesdecreases in proportion to the amount of toner already being held ontheir surfaces. Once a carrier granule can electrostatically accept nomore toner, it is said to be saturated. This saturation level is usuallyconsidered greater than the optimum toner concentration level desired intwo component development systems. Consequently, latent electrostaticimages developed with saturated two component developer appear to bedarker than desired. It has been found, however, that by providing asupplemental electrostatic force against which carrier granules mustcompete in order to attract and retain toner patricles, tonerconcentration of a two component developer mix can be reduced from thesaturation level to a level optimum for good development results. Asupplemental force which can be varied, as a variable potential source,will consequently permit selective control and regulation of tonerconcentration.

Summary of the invention It is, therefore, an object of the instantinvention to dispense toner into a two component xerograp'hicdevelopment system.

It is also an object of the instant invention to dispense tonerparticles into a xerographic development system equal to the amount oftoner depleted from the system through the development of images.

A further object of the invention is to electrostatically control thetoner concentration of developer in a xerographic development system.

A further object of the invention is to maintain optimum tonerconcentration in xerographic development zones.

A further object of the instant invention is to maintain equal tonerconcentration across xerographic development zones.

It is a further object of the present invention to add toner particlesto carrier granules in a two component development system in response tothe electrostatic properties of the developer.

These and other objects of the instant invention are obtained byapparatus for maintaining a quantity of charged toner particles betweena pair of screens or networks. At least one of the networks iselectrically biased to retain an electric field within the toning zonedefined by the network. When carrier granules are moved through thezone, they may triboelectrically attract and retain toner particles fromwithin the zone. In attracting toner particles, however, the carriergranules must compete against the electrostatic field within the zone.Consequently, individual carrier granules may only attract and retaintoner which would bring the concentration up to an optimum degree. Thisoptimum degree is less than their saturation level which would beachieved if the biased screens were not employed.

Brief description of the drawings For a better understanding of thenature of the invention, as well as other objects and further featuresthereof, reference is had to the following detailed description of theinvention to be read in conjunction with the accompanying claimswherein:

FIG. 1 is a sectional view of a xerographic reproducing machineembodying the principles of the instant invention with parts of thedeveloping and toner dispensing instrumentalities broken away forclarity and FIG. 2 is a sectional view of a reproducing machine similarto that shown in FIG. 1 with modified toner dispensing elements.

FIG. 3 is a sectional view of a reproducing machine similar to thatshown in FIGS. 1 and 2 with further modified toner dispensing elements.

Description of the preferred embodiments The illustrated embodiment asrepresented by FIGURE 1 shows a xerographic surface It formed in theshape of a drum and mounted for movement upon a main dnrm drive shaft 12for rotation in direction of the arrow. The drum and main drum driveshaft may be moved by any conventional power source, not shown. Themotion of the surface of the drum is such as to sequentially andcontinuously move the surface past the several xerographic processingstations as illustrated in FIG. 1. The elements of this machine are allconventional in the xerographic art with the exception of those at thedeveloping station which form the basis of the present invention. Forthe purpose of the present disclosure, the several xerographicprocessing stations in the path of movement of the xerographic surfacemay be briefly described as follows:

A charging station A at which a uniform electrostatic charge isdeposited on the photoconductive layer of the xerographic drum;

An exposure station B at which a light or radiation 3.- pattern of copyto be reproduced is projected onto the drum surface to dissipate thedrum charge in the exposed areas thereof to thereby form a latentelectrostatic image of the copy to be reproduced;

A developing station C at which a xerographic development materialincluding toner particles having an electrostatic charge opposite tothat of the electrostatic image, are moved into Contact with the drumsurf-ace, whereby the toner particles adhere to the electrostatic imageto form the xerographic powdered image in the configuration of the copyto be reproduced, and at which toner is dispensed into the developermaterial to replace that depleted from the developer mixture through thedevelop ment of images;

A transfer station D at which the xerographic powdered image iselectrostatically transferred from the drum surface to a transfermaterial or a support surface; and

A drum cleaning and discharge station E, at which the drum surface isbrushed to remove residual toner particles remaining thereon after imagetransfer, and at which the drum surface is exposed to a relativelybright light source to effect substantially complete discharge of anyresidual electrostatic charge remaining thereon.

Development takes place adjacent a main developer rocker assembly 14supported by opposed end faces 16. The end faces are each provided withapertures 18 for mounting the rocker assembly on the main drum driveshaft 12 adjacent the ends of the xerographic drum. A lower supportplate 20 interconnects the end faces adjacent the xerographicdevelopment zone 22. A reciprocatory motion is imparted to the rockerassembly by a motor 24- and pivoted linkage means 25 which interconnectsone of the end faces with the motor for imparting a rapid oscillation tothe rocker assembly. The end of the linkage assembly connected to theend face should be secured thereto at the center of percussion of the.rocker assembly for minimizing extraneous vibration.

Insofar as has been described, the development instrumentalities aresubstantially as described in my aforementioned copending applicationSer. No. 566,944, filed July 21, 1966.

When a quantity of two-component developer is located upon the supportplate 20 and a rapid reciprocation is impaited thereto by motor 24through linkage assembly 26, the vibrated developer will suspend itselfin a fluidized state throughout the development zone for contacting thesurface and developing latent electrostatic images which have beenformed thereon. A development electrode 28 is provided to define thelower face of the development zone 22. The development electrode asshown here takes the form of a screen of such mesh as to permit thedeveloper to freely flow therethrough. The development electrode isbiased to a potential slightly greater than that on background areas ofthe image to be developed for the minimization of background tonerdeposition. This would be positive in conventional systems. Thedevelopment electrode 23 serves another function in the instant deviceas will be later explained.

In the above-referred to former application, developer was gravity fedthrough the development zone for maintaining adequate tonerconcentration within the development zone. According to the instantinvention, however, this problem is overcome by virtue of the noveltoner dispenser.

According to the instant invention, the rocker assembly 14- is formedwith a supplemental screen electrode 30. This electrode is a supportmeans to retain a quantity of developer mix adjacent the image for itsdevelopment. It is preferably constructed concentric with respect to thesupport plate 20, xerographic surface 10 and development electrode 28.The supplemental screen electrode 30 is of such mesh as to permit freeflow of toner particles, but not carrier granules therethrough. Like thedevelopment electrode 28, the supplemental electrode is constructed ofan electrically conductive material for supporting an elcctric potentialthereon. The area beneath the supplemental electrode 30 and above thesupport plate constitutes a sump 32 for the retention of a supply oftwo-component developer mix having an excess quantity of tonerparticles. The region between the development electrode 28 andsupplemental electrode 30 is the toning zone 34. Since no continuingflow of developer through the development zone is shown, as there was inmy aforementioned copending application, retaining lips 36 are providedon the supporting plate 20 between the end faces 16 for restricting themovement of the fluidized developer from beyond the development zone.

When the developer mixture is vibrated into a fluidized state during thedevelopment of images, toner is continuously being lost from thefluidized developer material by the development of xerographic images.It is intended that a quantity of toned developer be located above thesupplemental electrode 30 for movement between the supplementalelectrode 30 and xerographic surface 10. This developer is used fordevelopment of images and is retained within the toning zone 34 anddevelopment zone 22 since the mesh of the supplemental screen 30 willnot permit the movement of carrier thcrebeneath.

As the developer rocker assembly 14 vibrates during normal operation, aquantity of toner particles from within the sump will be charged due tointeraction with the quantity of carrier within the sump 32. Thevibrations act to permit a quantity of these charged toner particles torise through the supplemental electrode 30 into the toning zone 34. Itis this same vibrational force which moves the two-component developerabove the supplemental electrode 30 into and out of contact with thexerographic surface 10.

In order to eifect the optimum toning of carrier particles trappedwithin the zoning and development zones 34 and 22, it is necessary toelectrically bias the electrodes 28 and 30. This is done by means of afirst variable potential source 38 adapted to hold the developmentelectrode 28 at a potential slightly above the potential on backgroundareas of the surface to be developed. This would be approximately onehundred volts positive in conventional xerographic systems. The secondvariable potential source is adapted to hold the lower or supplementalelectrode 310 at a higher positive potential with respect to thedevelopment electrode 28. In the instant system, wherein a spacing isemployed between the xerographic surface and the development electrode28 with a A" spacing between the two electrodes, a 4,000 volt bias onthe supplemental electrode has been found suitable for producing thedesired toner migration.

When such a system is employed, and negatively charged toner particlesare sifting into the toning zone 34 from the sump 32 for developingpositive images, the development electrode will exhibit an electricallyrepulsive force on the charged toner particles. This will keep tonerparticles, unassociated with carrier granules, from entering thedevelopment zone 22. As undertoned carrier granules pass into thevicinity of the charged toner particles, they will attract the chargedtoner particles and retain them up to the point where the carriergranules are optimumly toned. They will not attract toner particles upto their saturation level inasmuch as the force of the developmentelectrode 28 acts against the force of undertoned carrier granules,tending to urge the toner particles back toward the sump. It can thus beseen that the variable ability of potential sources 38 or 40 could varythe repulsive force on the toner particles to control the amount oftoner particles the carrier granules can accept. This in turn could beemployed to control image density. This process is in continual effectas carrier granules are constantly moved in their fluidized state fromthe xerographic surface where they deposit toner on the image beingdeveloped and back to the toning zone for attracting additional tonerfor subsequent image development.

The purpose of the sump is to provide a large quantity of tonerparticles for replacing that lost from the system through thedevelopment of images. It has been determined, however, that usingconventional two-component developer comprising carrier granules andtoner particles in the sump region has met with certain limitingfactors. When an overly large quantity of toner is positioned within thesump, there is a tendency for the heavier carrier granules to work theirway toward the bottom of the developer of the sump upon extendedagitation. When this happens, there will be an upper layer of tonerparticles entering the toning zone from the sump in an unchangedcondition due to inadequate contact with the carrier granules. This canbe overcome by using a lesser quantity of toner or by replacing theconventional carriers in the sump with larger pieces of material capableof imparting a triboelectric charge to the toner moving into the toningzone. Another manner in which this could be done would be to employ anadditional screen within the sump slightly beneath the supplementalscreen. By making this additional screen with a surface of a carriercoating material, toner sifting upward toward the toning zone wouldcontact the screen surface for charging the toner to thereby insuretriboelectric charging of all toner particles entering the toning zone.

Shown in FIGURE 2 is a second machine which is similar to that shown inFIGURE 1 except for a modified lower or supplemental screen. The purposeof this modication is to insure the complete charging of all tonerparticles entering the toning zone. All of the elements of this secondembodiment are designated by the same reference numerals of the firstembodiment except those which structurally differ from the firstembodiment.

The supplemental electrode screen 30 of the first embodiment is replacedin the second or FIG. 2 embodiment by an undulating supplemental screen42 with electrically insulating caps 44 covering the upper portions ofthe screen 42. As the developer rocker assembly 14 is vibrated causingtoner particles to sift upwardly from the sump 32 into the toning zone34, the toner-charging carrier granules within the sump are caused toseep downwardly within the developer mix in the sump. These carriergranules thus congregate in a region close to the suppor plate 20 in thelowermost regions of the sump 32. This action is accompanied by arelative rising of the toner particles into the upper portions of thesump 32 which is adjacent the caps 44. The caps 44 prohibit the movementof uncharged toner particles from the upper regions of the sump to thetoning zone. Thus, the toner which will be continually rising upwardlyfrom the sump to the toning zone 34 will be those toner particlesadjacent the lower regions of the sump which are in an agitatingrelationship with the carrier granules from the lower regions of thesump. This embodiment thus insures more complete charging of those tonerparticles rising into the toning region than does the first embodiment.

In order to operate the machine of either of the disclosed embodiments,it is first necessary to activate a general cycle initiating means, notshown. This will act to energize the various processing stations asdescribed above and to move the xerographic drum surface past eachstation in a continuing and automatic cycle of operation. The generalcycle initiating means Will also establish the biases on the variouselectrode elements as well as cause the rapid oscillation of thedeveloper rocker assembly 14.

The developer rocker assembly 14 is set into a vibrating state with aquantity of overtoned developer in the sump 32 and a quantity oftwo-component developer in the toning zone. The developer within thetoning zone will be agitated into a fluidized state for contacting anddeveloping latent electrostatic images on the xerographic surface.Concurrently therewith, the carrier within the sump will agitate thetoner therewith to thereby eifect a charging of that toner within thesump. The same vibration will also cause the charged toner within thesump to move upwardly through the supplemental electrode screen 30 or 42to suspend itself in the toning zone. A portion of the charged tonerparticles will also electrostatically attach itself to the supplementalscreen but can be removed therefrom by a tendency to triboelectricallyattach themselves to undertoned carrier granules.

When negative particles are employed to develop positive images on thedrum, a positive bias on the development electrode 28, lower than thaton the supplemental electrode 30, will act as a repulsive force againstthe toner in the toning zone to prohibit its movement into thedevelopment zone 22. When, however, undertoned carrier granules aremoved through the toning zone, they will attract additional tonerparticles to their surface up to the point that they will becomeoptimumly toned. This degree is somewhat less than the saturation tonerconcentration for the carrier granules since the development electrodeis exhibiting a force tending to repel the charged toner particles backto the supplemental electrode and sump.

As toner is lost from the developer mix through the development ofimages, the carrier granules are moving into and out of the toning zonefor attracting and retaining additional charged toner particles. Theseadditional charged toner particles are in suspension within the ton ingzone during vibration. A large quantity of such toner particles,however, remains electrostatically attached to the intermediate screens36 or 42. The charge from the undertoned carrier granules is suflicientto attract these toner particles from the screen as needed.

The second embodiment operates in the same fashion as the firstembodiment except that the toner rising from the sump will be moreuniformly and completely charged triboelectrically due to beingcontacted by the heavier concentration of charging carrier granuleswhich tend to congregate in the lower region of the sump 32.

In either embodiment additional toner can be added to the systems as byproviding a removable section in one of the end faces 16 of the rockerassembly. Thus, when the rocker assembly is at rest, the end face can beopened adjacent the sump for manually inserting additional tonerthereto. It is also possible to add additional toner to the lower sumpregion by a flexible hose coupling linking a raised toner supply to thesump. Furthermore, it is possible to create a flow of developer acrossthe development zone in a manner similar to the developer flow disclosedin my aforementioned copending application.

The third or FIG. 3 embodiment of the instant invention involves amodification of the FIG. 2 embodiment. In this particular embodiment,the support plate 20 is mounted onto retaining lips 36 and end faces 16by suitable electrically insulating barriers 418. The upper face of theplate 20 is covered with an insulating layer 50 as of any of theconventional carrier coating materials described in US. Patent No.2,618,551. Development electrode wires 52 running across the length ofthe development zone are used in place of the development electrodescreen 28 of the first two embodiments. A suitable source of potential38 creates an electrical bias between the substrate of the xerographicsurface and the development electrode wires 52. A second source ofpotential 4-0 creates an electrical bias between the developmentelectrode wires 52 and plate 20.

The intermediate screen 42 of the first two embodiments is replaced by astiff electrically insulating screen 54, as of saran or the like. Thisscreen, like the intermediate screens of the first two embodiments, isapertured sufficiently to permit the ilow of toner, but not carrier,therethrough. The cap portion 44 may be formed integrally with such ascreen in a manner similar to the FIG. 2 embodiment. The toning zone ofthis embodiment extends between electrode wires 52 and insulating screen54. The electrical field within the toning zone of this third embodimentis not created by the intermediate screen. Rather, it is created betweenthe development electrode wires 52 and plate 20. The field within thetoner loading zone between screen 54 and the drum surface 10 is achievedby a proper high voltage, as for example, 5,000 volts positive on thelower plate 20. The insulating layer 50 on the lower support plate 20assists in charging the toner and also serves as a dielectric barrier topermit the use of high field generating potentials between wires 52 andplate 20 to eliminate the chance of electrical breakdown therebetween.

The third embodiment has an advantage of permitting a flow of developerfrom the development electrode wires back to the sump zones. This isbecause the field in the toning zone extends from the developmentelectrode wires down to the lower plate 20 rather than merely stoppingat the intermediate screen. The electrostatic retention of charged tonerparticles on a charged intermediate screen is eliminated.

In all three embodiments, the variable potential source permitsadjustment of the potential on the various con ductive elements to thuspermit variations in the rate of toning and consequently the imagedensity of developed xerographic copy.

It has been disclosed that the present invention may be readily carriedout in a fluidized bed development systern of the oscillatory type. Itshould also be understood that the principles herein are equallyapplicable to other development systems including fluidized beds of thehorizontally or vertically reciprocating as well as orbital types. Othertypes of conductive electrode networks suitably apertured could beemployed as substitutes for the electrode screens to effect the sameresult. And although specific operational values have been referred toin order to illustrate voltages, distances, and polarities, capable ofpermitting the practice of the instant invention, these values should beconsidered as illustrative only inasmuch as the invention is operablethrough a wide range of operating parameters.

While the present invention as to its objects and advantages has beendescribed herein as carried out in specific embodiments thereof, it isnot desired to be limited thereby; but it is intended to cover theinvention broadly within the scope of the appended claims.

What is claimed is:

1 In a xerographic development system of the type having support meansto retain a quantity of developer material including carrier granulesand charged toner particles adjacent a surface bearing a latentelectrostatic image to be developed, means to vibrate the support meansto thereby suspend the developer material on the support means in afluidized state in contact with the image for the development thereof,an apertured development electrode in operative proximity to the imageand means to electrically bias the development electrode to the samepolarity as that on the image, improved toner dispensing apparatuscomprising means to create an electrical bias between the support meansand the development electrode tending to repel charged toner particlesfrom the development electrode towards the support means and means tointroduce toner particles, charged to a polarity opposite from that onthe image to be developed, into a toning zone between the developmentelectrode and the support means so that undertoned carrier granulesvibrating between the image and support means can triboelectricallyattract and retain additional toner particles up to an optimum tonerconcentration by overcoming the electrostatic force of the developmentelectrode tending to repel the charged toner particle towards thesupport means.

2. The apparatus as set forth in claim 1 wherein the support means is anelectrically conductive member apertured to permit the movement of tonerparticles but not carrier granules therethrough.

3. The apparatus as set forth in claim 1 wherein the support means is anelectrically conductive member and the means to create an electricalbias is a source of potential electrically interconnecting thedevelopment electrode and the support means.

4. The apparatus as set forth in claim 1 wherein the support means is anelectrically insulating screen apertured to permit the flow of toner butnot carrier therethrough.

5. The apparatus as set forth in claim 4 and further including anelectrically conductive underplate capable of supporting a supply oftoner particles and wherein the means to create an electrical bias is asource of potential electrically coupling said development electrode andsaid underplate.

6. The apparatus as set forth in claim 2 and further including sumpmeans on the side of the support means remote from the developmentelectrode for feeding charged toner particles into the toning zone.

7. The apparatus as set forth in claim 6 and further including means tovibrate the sump means for fluidizing the charged toner particles tothereby effect the migration of charged toner particles from the sump tothe toning zone.

8. The apparatus as set forth in claim 7 and further including meansinterconnecting the support means and sump means for concurrentvibration.

9. The apparatus as set forth in claim 8 wherein the sump means containsa supply of toner particles as well as means to triboelectrically imparta charge to the toner particle.

10. The apparatus as set forth in claim 9 wherein the support means is ascreen with an undulating cross-sectional configuration and furtherincluding imperforate means over the portions of the undulating screenclosest to the development electrode so that toner particles enteringthe toning zone from the sump enter from the lower region of the supplyof toner particles.

References Cited UNITED STATES PATENTS CHARLES A. WILLMUTH, PrimaryExaminer.

P. FELDMAN, Assistant Examiner.

